Soutli African Fossil Reptiles and Amphibia. 207 



pit in the occipital condyle. The front face is lightly channelled 

 horizontally by two small grooves, each ending in a foramen for 

 a vein. 



The inside of the brain-case has been wholly freed from matrix, 

 and shows the positions of the foramina for the exit of the cranial 

 nerves. In front of the foramen magnum the opening is narrow 

 for a short distance, being bounded laterally by the exoccipitals. 

 In front of these it broadens and its plane is horizontal for about 

 20 mm., when its base slopes abruptly upwards. The exit for 

 the Xllth nerve is seen to pass through the exoccipital almost 

 at the top of the condyle. Anterior to the exoccipitals the floor 

 of the brain-case falls away laterally to the foramen jugulare, 

 nerves IX-XI passing out through an ill-defined broad groove 

 in the floor, which expands laterally. Anterior to this, the hori- 

 zontal portion of the floor has a strongly marked rounded median 

 ridge which separates the two inner ear-openings from one another. 

 These lie fairly close together in pits excavated wholly in the 

 floor of the brain-case. There is no abrupt line of demarcation 

 between this opening and the proximal end of the course of the 

 IX-XI nerves ; and one may consider that there is one large 

 excavation shallow behind and deeper in front the former 

 passing to the foramen for the exit of nerves IX-XI and the anterior 

 portion being the opening into the vestibule. 



Anterior to the vestibule the, floor of the case slopes upward 

 forming a plate about 40 mm. long in the middle, longer at the 

 sides, and thinner above than below. The front of this plate 

 slopes backwards and downwards until it forms the base of the 

 pituitary fossa, in front of which it rises again almost vertically. 

 In a specimen which may be an immature skull of Gorgonognathus 

 this plate is high and vertical behind the pituitary fossa and is 

 divided by an open median vertical suture. 



A fracture shows the inner ear to be connected with the fenestra 

 ovalis by an hour-glass shaped passage about 25 mm. long. This 

 passes mainly outwards and slightly downwards. The constriction 

 in the middle is very pronounced and nearer the inner than the 

 outer end. The fenestra ovalis is very wide, wider than the upper 

 end of the vestibule. It is separated from the foramen jugulare 

 by the process of the basioccipital which forms its anterior border. 

 The fenestra ovalis is entirely surrounded by bone, thus differing 

 from that of Diademodon. At the upper end of the ear the course 

 of the semicircular canals cannot be distinguished. The foramen 

 for the Vllth nerve has not been seen. 



17 



